Runs a checkpoint of the entire application (e.g. browser) window.
promise = eyes.checkWindow(tag, matchTimeout)
The tag defines a name for the checkpoint in the Eyes Test Manager. The name may be any string and serves to identify the step to the user in the Test manager. You may change the tag value without impacting testing in any way since Eyes does not use the tag to identify the baseline step that corresponds to the checkpoint - Eyes matches steps based on their content and position in the sequences of images of the test. See How Eyes compares checkpoints and baseline images for details.